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San Andreas Fault. Introduction. We live next to this fault It’s active It has a history of major earthquakes We had better know something about it ..so that we can better prepare. Features-1. Not recognized (in total) until ~1940
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Introduction • We live next to this fault • It’s active • It has a history of major earthquakes • We had better know something about it • ..so that we can better prepare
Features-1 • Not recognized (in total) until ~1940 • Not recognized as a plate boundary until ~1970 – plate tectonic theory had to happen first! • Named after Lake San Andreas (SW of San Fransico) following the 1906 earthquake
Features-2 • Plate boundary between N. American and Pacific plates • Motion is transform with the Pacific plate moving northward
Features-3 • Active since 23.5 my BP; total = 315 km • Long-term rate = 1.3 cm/year • NOTE – there have been other strands and similar faults have occurred in the region since ~~60 my BP; ~~480 km offset of Baja California peninsula
Pallett Creek Work of T. Sieh, ~1987 Ph.D., California Tech.
Key to understanding • C-14 dating of organic material • Carefully relating ages to offset of pond sediments
Summation of findings • Covers 1700 years • Median frequency = one per 132 years • Range 50 – 500 years
Features • 1857 (before reliable, common seismometers and reproducible results) • Magnitude ~8.0 • Offset near epicenter ~ 9 m
Rupture • and felt area